This project investigates the environmental and physiological regulation of the pineal gland, exclusive of transmembrane and intracellular regulatory mechanisms (see Z01-HD 00095-16 LDN). The pineal gland is part of the melatonin rhythm generating system, a neural circuit which includes a circadian clock in the suprachiasmatic nucleus (SCN); the SCN is reset and entrained by light acting through the eye. It has been proposed that the SCN - pineal circuit passes through the paraventicular nucleus of the hypothalamus (PVN). This past year work was completed which supports this with the demonstration that electrical stimulation of the PVN stimulates the production of melatronin at a near physiological rate. In other studies, the photoneural regulation of pineal rhodopsin kinase and phospholipase C have been studied; and the developmental appearance of both phospholipase C and Na+/K+-ATPase has been examined. It has been discovered that Na+/K+-ATPase develops after birth, as indicated by both ouabain binding and ATPase activity. This indicates that another mechanism might generate membrane potential before this time.